1. Field of the Invention
This invention relates to tape position display apparatus and, more particularly, to novel and highly-effective tape position display apparatus for use with a VTR (video tape recorder), an audio tape recorder and the like.
2. Description of the Prior Art
In the prior art, there are two basic types of tape position display apparatus. In one type of conventional tape position display apparatus, a roller is mounted in contact with a magnetic tape so that the roller rotates whenever the tape runs. A rotation detector detects rotation of the roller and produces detection pulses proportional to the rotation of the roller. A count display apparatus is driven by the detection pulses produced by the rotation detector thereby to display the instantaneous position of the tape (with respect, for example, to the magnetic head(s)). In the other type of conventional tape position display apparatus, a position signal (CTL signal) is recorded in a pattern that repeats at equal distances along an edge of the magnetic tape extending in its longitudinal direction. While the magnetic tape is transported, the position signal is reproduced therefrom by a magnetic head, and the count display is driven by detection pulses derived from the magnetic head thereby to display the instantaneous position of the tape.
The former conventional tape position display apparatus has the advantage that tape position detecting pulses of high reliability can be produced continuously. However, it has the drawback that, if the magnetic tape and the roller slip with respect to each other or the magnetic tape becomes slack, the detection accuracy of the tape position detecting pulses is reduced.
The latter conventional apparatus avoids the drawback of the former apparatus. However, if a dropout occurs in the playback of the position signal, the detection accuracy of the tape position detecting pulse is inevitably reduced.
There is also in the prior art a hybrid tape position display apparatus, which is formed of the combination of the two basic types of apparatus described above and which therefore improves the accuracy of the tape position detecting pulse (see a published, examined Japanese patent application No. 9504/1983).
However, such hybrid apparatus also has certain drawbacks. Specifically, as explained in greater detail below, it is impossible to determine whether or not the pulses that result from mechanically detecting the tape transport, and which give a first indication of the position of the tape, are out of phase (e.g., delayed) with respect to the pulses that result from reproducing the position signal recorded on the tape, and which refine the indication provided by the first-named pulses. It is also impossible to determine the magnitude of the phase difference, if any, between the two sets of pulses. Furthermore, if the phase difference between the first and second pulses could be determined and were large, the phase of the tape position detecting signal finally obtained would be suddenly and drastically changed by the second pulses.